This invention relates to a rechargeable device for storing and, when desired, releasing hydrogen. Among other applications, the device can be used in the energy generation or transportation industries.
A hydrogen economy has become a National vision. xe2x80x9cHydrogen has the potential to solve two major energy challenges that confront America today: reducing dependence on petroleum imports and reducing pollution and greenhouse gas emissions. There is general agreement that hydrogen could play an increasingly important role in America""s energy future. Hydrogen is an energy carrier that provides a future solution for America.xe2x80x9d A National Vision of America""s Transition to a Hydrogen Economy to 2030 and Beyond, based on results of the National Hydrogen Vision Meeting, Washington, D.C., Nov. 15-16, 2001xe2x80x94United States Department of Energy February 2002
For mobile hydrogen powered systems, i.e., fuel cell powered electric vehicles, hydrogen must be obtainable.
In U.S. Pat. No. 6,305,442, issued to Ovshinsky, a hydrogen infrastructure system is proposed. It teaches hydrogen bound to a metal alloy hydride. Release and storage of hydrogen bound to the hydride is a process which requires energy. Ovshinsky states that a major drawback of hydrogen as a fuel in mobile uses, such as powering of vehicles, is the lack of an acceptable lightweight hydrogen storage medium. Ovshinsky identifies hydrogen vessels as heavy, and having a xe2x80x9cvery greatxe2x80x9d explosion/fire hazard. Further, Ovshinsky identifies pressurized tankers as an unacceptable medium for transporting all but smaller quantities of hydrogen due to susceptibility to rupturing and explosion.
Accordingly, a hydrogen storage medium without necessitating the use of hydrides that is relatively lightweight and safe would be desirous.
A hydrogen replenishment system is taught in U.S. Pat. No. 6,432,283 issued to Fairlie et al. Fairlie teaches an electrolytic cell which produces oxygen gas during gaseous hydrogen production. The Fairlie system vents gaseous oxygen during the dispensing of hydrogen creating the explosive risk of hydrogen-oxygen mixtures. Accordingly, it would be desirous to have a refueling system wherein gaseous oxygen is not produced when the system is dispensing hydrogen thereby avoiding possible mixing of gaseous hydrogen and gaseous oxygen.
Additionally, hydrogen gas produced from the electrolytic cell described by Fairlie et. al is produced at an elevated temperature. Fairlie et al teaches away from the use of hydrogen storage tanks identifying them as a xe2x80x9cpotential safety riskxe2x80x9d and teaches the simultaneous generation and dispensing of hydrogen. It is a well established principal of physics that the density of hydrogen gas is inverse to the temperature. In-fact, Fairlie notes that there is a problem of obtaining a false value of a high pressure fill (full tank) if the filling is too rapid due to temperature increase within the tank. At a constant pressure, the greater the temperature of the gaseous hydrogen, the lower the density of the gaseous hydrogen thus creating a false value. Fairlie""s temperature management solution is to wait for the external vessel to cool down by modulating the rate of fill.
Achieving a full fill, as noted by Fairlie, is particularly applicable to hydrogen fueled, fuel cell powered vehicles. The operating range (distance) a fuel cell powered vehicle can potentially travel is related to the quantity of hydrogen on board. A second variable equally applicable to promoting the operation of fuel cell powered vehicles is that sufficient quantity of hydrogen to support a preselected operating range is dispensed in a time frame which is within the xe2x80x9cconvenience expectationsxe2x80x9d of an end user. It is therefore desirous to have a hydrogen refueling station which manages the temperature of the gaseous hydrogen to minimize reductions in rate of fill.
Trailers transporting pressurized cylinders of gas are known in the art. Large semi-tanker/trailers for transporting gaseous fuels are also known in the art. Semi-tankers are not a convenient method for providing transportable hydrogen for refueling. Specifically, the use of a semi-tanker requires a specialized driver""s license and due to weight and size restrictions, a semi-tanker may be limited to use on some roadways and may have limited access to some locations. A small trailer suitable for towing by a passenger vehicle which can transport upwards of 35 kg of hydrogen would solve many of the limitations of a semi-tanker.
A refillable hydrogen refueling station within an enclosure that can dispense upwards of 35 kg of hydrogen is taught. Gaseous hydrogen is stored at high pressure without the use of heavy tanks, hydrides or metal alloys. The refueling station within the enclosed one can be trailer supported. The trailer supported enclosure or the refueling station within an enclosed trailer can be towed by a passenger vehicle.
The energy density of a system for transporting hydrogen could be measured as grams/liter of stored gas as done by Ovshinsky in the U.S. Pat. No. 6,305,442 patent, however, such a measurement can be misleading when transportability of the hydrogen is a factor. For transportable hydrogen, a useful measure of energy density is grams of hydrogen per pound (gms/lb) of the gross weight of the transportable system.
The hydrogen refueling station accepts a hydrogen feed stock, increases the pressure of the hydrogen up to a desired pressure, and stores the hydrogen in one or more tanks for later dispensing. Distribution of the hydrogen is through a reversible connector that can dispense the hydrogen from the tanks to a receiving tank or apparatus.
In one embodiment, the hydrogen refueling station is self-refilling. It has a hydrogen producing subsystem which can also refill the tanks within the refueling station""s hydrogen storage subsystem. The self-refilling function is provided by a hydrogen generating device such as an electrolyzer or electrolytic cell.
To reduce the risk of the gaseous oxygen, produced as a by-product of hydrogen generation, from mixing with gaseous hydrogen the hydrogen refueling station can be operated to produce and store hydrogen in the storage tanks at a time remote and distinct from the dispensing of the hydrogen. Connections from the hydrogen producing subsystem to the hydrogen storage tanks are fixed and easily monitored for leaks as opposed to the temporary connections made by the reversible connector.
Common to the embodiments described herein is temperature management of the hydrogen. Hydrogen produced by an electrolyzer or electrolytic cell is produced at temperature elevated above ambient. This elevated temperature decrease the density of the hydrogen gas. To provide a higher density of the hydrogen gas the elevated temperature of the hydrogen produced can be reduced by cooling the hydrogen as it flows and not simply reducing the rate of fill.
Temperature management can result in higher density of the hydrogen gas, which equates to more grams of hydrogen. The quantity of hydrogen dispensed to the end user, and the rate at which it is dispensed, should meet the reasonable convenience expectations of the end user.
Most preferably the time it should take to refill a fuel cell powered vehicle will be similar in duration to the time it takes to refuel an automobile with gasoline. Further, the quantity of hydrogen dispensed should have the potential to power a fuel cell powered vehicle a range of travel also within the reasonable convenience expectations of an end user.
In some instance the hydrogen storage tanks may be by-passed and the hydrogen from the hydrogen producing subsystem cooled and dispensed directly to an end user.
The electrolyzer may be powered by renewable source including to not limited to wind, hydroelectric and solar. Electricity from turbines and/or Photovoltaic panels can be connected to the electrolyzer or electrolytic cell to support hydrogen generation.